This article takes an in depth look at electric heaters and their advantages.
It will cover topics such as:
Electric heating is produced by using a known resistance in an electric circuit. This placed resistance has very few free electrons in it so it does not conduct electric current easily through it. When there is resistance in the flow of electrons, then this resistance will produce heat. The heat produced will be the heat energy required for electric devices to work. Electric heating is the most efficient but an expensive process because this resistant heating will take a lot of electrical energy. The price of electricity is too high compared to other energy resources such as water, gas and fossil fuels. Compared to the other factors such as purchasing price and installation of these electric heaters is quite less that attracts the buyers. When it is used for domestic purposes it is generally insulated with some plastic materials to save the residents from electric shocks and also to minimize the energy dissipation.
Electric heaters are made up of a heating core radiator that heats up when the electric current enters into the device. These cores are two types that are used in heaters and radiators. The core types are oil filled core and a dry core. The dry core is made up of ceramic that makes it light weighted and leak proof. Ceramic or dry core radiators are energy efficient and can retain heat well; this heat retention plays an effective role in its efficiency. The radiator's body is made up of aluminum or steel which helps in the dissipation of energy.
The other core that is oil filled radiator is filled with oil, but there is no need to refill it because the oil in this radiator is heated. This results in the thermal liquid in the reservoir lasting the entire lifespan of the product. The resistor coils can be exposed mounted on the insulators; metallic resistors may be embedded in the refractory insulation with an enclosure of protective metal or may be a printed circuit with a glass case. There are also fins present in this electrical device that help to increase the area of heat dissipation.
All the electric heaters have a heating element that is an electrical resistor. They work on the principle of Joule’s law. These resistors convert the electrical energy into heat energy by emitting radiant energy. Resistors may be made up of metal alloy wires, non metallic carbon compounds, or any printed circuits. Modern electric devices use nichrome metal as heating elements. The electric heaters use nichrome metal wires as active elements with ceramic insulation.
There are generally three types of electric resistance heating wires that are used in modern resistors.
Open wire is a nickel chromium resistance wire that is placed on ceramic or mica insulation. The protection part of this wire is really important. The user or any metal object should not be in contact with this wire because of severe electric shocks.
Open ribbon wire is the same as open wire in material but it has more exposed surface area that will result in electric shocks if anything comes in contact with it.
Tubular Cased Wire is also a nickel chromium resistance wire that is protected with magnesium oxide powder that is further enclosed in a heat resistance steel tube. This will protect from electric shocks. It will also be long lasting.
The electric heaters work on the principle of joule’s law. These are the single units that use electrical elements that produce heat to warm the core of the heater. The electric heater works when an electric current passes through the resistors that are present in the heater. These resistors will heat up by the flow of electric current and give off their energy in the form of heat. The heat will dissipate in the surrounding area and the core of the heater will warm up giving off the desired temperature across the space. The electric current entered the resistors and will charge up the cathode in the electron tube resultantly giving off heat.
There are three modes of heat transfer conduction, convection and radiation. The heat processing is different for all these three methods. Let’s discuss them one by one.
This is the method of heat transfer in which one heated molecule will transfer the heat onto the next molecule or substance. Thus the energy is transferred from one substance to another or any two substances in contact with each other. Many electrical devices use this method of heat transfer. The rate of heat conduction depends on the temperature gradient. It means higher the temperature, higher the conduction rate.
Convection mode of heat transfer is used in immersion water heaters of low temperature heating equipment. The air comes in contact with the heated element which results in the expansion of hot air. This hot air will rise above in the room and the cold air will come in contact with the heated radiator. Thus it is the circulation of heated and cold air across the space. This movement of hot and cold air across the whole container or the room will help in the heating of air or water. The rate of convection process depends on the temperature above the heated element, size of the heater surface and also partly on the position of the heater.
Radiation is the heat transfer process in which heat is radiated from the heated medium and reaches the other substances without heating the medium or anything between these two. Most electric heaters rely on this medium of heat transfer and radiates the heat energy to warm up the surroundings.
There are many different types of electric heaters that have specific functions and design that makes them suitable to work in different environments such as homes, offices or industries also. Some of the types of electric heaters are air heaters, ceramic heaters, cartridge heaters, band heaters, coil heaters, drum heaters, industrial heaters, kapton heaters and many more.
Air heaters are the type of electric heater that uses air for heating the surroundings. In this category are the forced air products, radiant, and space heaters. The forced air products are moderate and control the air temperature by circulating the air with the help of a fan or a blower of the heater. Forced air heaters work in a way that the cold air enters the air heater and then comes back at an elevated temperature that is the hot air. The radiant air heater works with the radiation coming off from the heated object and then convection cycle helps in circulating the hot air around the surroundings. Whereas the space heaters are the self contained devices that work with any of the above mentioned modes.
The process of heat transfer in an air heater is by convection. It is a method in which heat is transferred through a fluid or a medium. This medium will create a convection current that is either free flowing or forced. In forced flow convection, the circulation is either generated by a pump or fan. Whereas the free flowing convection current is solely dependent on the temperature fluctuation and concentration gradients.
Air heater is a broad type with about 7 options. They are duct heaters, enclosure heaters, forced air heaters, heat torches and flame heaters, radiators, space heaters or room heaters, and tubular heaters.
Duct heaters are used to produce heat in gas streams. These are installed in the middle of the gas stream or moving air so that the passing air becomes heated while moving from the heater.
These enclosure heaters are used only for enclosures. They are designed to prevent freezing, provide protection and control humidity.
Forced air heaters use forced convention to move the air from the heat source using a blower or a fan.
These two devices emit concentrated flames or streams of very hot air or gas. Heat torches and flame heaters are mostly used in industry uses.
This type of air heater has coils which have heated, circulated liquids such as oil, hot water or steam.
Space heaters or room heaters are designed specifically for indoors and it does not emit dangerous pollutants or poisonous gases in the surroundings. Additionally these are portable.
Tubular heaters are generally used in customizing heating applications. Tubular elements can be bent into different shapes.
Band heaters are the heating devices that are ring shaped and can be clamped around the cylindrical heating elements. The band heaters are clamped on the outside of the heating elements and transfers heat from the outside. The mode of heat transfer in band heaters is conduction. Some band heaters are clamped on the inner diameter of the heating elements. Usually, they are equipped with ceramic or mineral insulation that helps in heat loss reduction to the environment.
For the best working of band heaters there are some parameters that are necessary to consider. These include maximum optimum operating temperature, voltage required or sheath temperature. Maximum operating temperature of the band heater is the temperature required to reach the sheath covering the heater. AC voltage is the minimum amount of alternating current that is required for heater operation.
Important dimensions of band heaters that are to be considered are inside and outside diameter of the band, thickness and width of the band. It is important to keep the same diameter inside of the band and outside of the cylinder where the band is to be attached.
The band heaters use a protective covering or a sheath for the heating elements. The protective sheaths can be any material such as aluminum, brass, copper, iron, nickel alloy, steel or stainless steel.
The band heaters are insulated with special materials to reduce the heat loss to the environment. The materials could be ceramic insulation, mica insulation, fiberglass insulation or no insulation is also an option. There are certain band heaters that have more than one type of insulation. The un-insulated material can be used in premium areas but the un-insulated band heaters are not energy efficient. The ceramic insulation is a good one to use because it can resist chemicals and heat. Ceramics that are made up of non metallic materials such as clay are good to use because they are hardened by high temperatures. Another insulating material is mica that has a good heat and acid resistance and also good insulating properties. Mica insulated band heaters are very efficient and good to use.
Band heater features are cooling options, probe holes, cut outs on the bands, expandable heaters. The band heaters are attached or clamped with the heating material. There are many clamping options from which we can choose. The examples of mounting are bent up flange or tab, built in strap, separate straps, barrel nuts and wedge lock or mounts.
Termination type means the methods that are used for making electrical connections to the heater. Some band heaters have multiple options of termination such as insulated leads, armour cable leads, metal braided leads, flexible conduit leads, parallel screw terminals, terminal boxes, and quick disconnects.
The cylindrical shaped heaters are the cylindrical shaped ones with resistant heating elements. The heating element of the cartridge heater is insulated to prevent the sheath from touching the heating element. This sheath or sleeve that encapsulates the heater also provides a protective barrier. The cartridge heaters are usually inserted into the heated material and its cylindrical shape is used in many applications.
There are certain specifications that are required before selecting cartridge heaters such as maximum operating temperature, material of sheath, voltage required, density of the sheath, watt density, and other features. Maximum operating temperature of these heaters exceed up to 1500°C when used for industrial purposes such as melting, casting or molding. Important dimensions of these heaters are nominal diameter and cartridge length or heated length.
Sleeves, sheath or jacket is the protective material that covers the heating material of the heater. This sheath can be made of any type of material such as aluminum, iron, copper, nickel alloy, brass, stainless steel or steel. All of these sleeve materials have different and specific properties. Insulation of cartridge heaters are either ceramic insulation, mica insulation, fluoropolymer insulation, fiberglass, or magnesium oxide insulation. Ceramic insulation is made of non metallic material which will get hardened by high temperature. Mica insulation is made of silicates that are colored. Both are resistant to chemicals and acids. Flouropolymer insulation is used in applications where there are superior chemicals involved. Fiberglass material is now widely used because it is strong, durable and resistant to caustics. Magnesium oxide has a high melting point and is resistant to high temperatures.
Flat ceramic fiber heaters are made of iron chrome aluminum heating elements and a thick layer of ceramic fiber insulation encased in a non-curved box. The ceramic fiber heaters can be made in many shapes and sizes and can be customized into any other shape. Ceramic heaters are faster in heating. Have great temperature uniformity, recovery rate and it can be cooled down faster than other heaters. Configuration of ceramic fiber heaters has several options such as fully heated means all the sides of heater are heated, unheated sides, or all edges insulated. Other specifications include maximum operating temperature, AC voltages and the watt density.
Heating coils of ceramic fiber heaters are available in different options; heating coils can be fully embedded within insulating material or may be partially embedded in it. These embedded coils have many advantages including protecting it from media splatters which can lead to fuming or sparkling. Usually, these flat ceramic fiber heaters cannot reach high temperatures due to partially exposed coils.
Coil heaters, also known as cable heaters, are the elongated heaters. These heaters are made from the uncoiled segments of square or round tubular heating elements. They can be straight in shape or can be modified into any desired configuration such as star shaped or spiral wound. The configuration is modified according to the needs of its application or it can be formed in a pattern that increases its surface area or capability of heat transfer. These coil heaters have a non metallic insulated sheath that protects it from overheating and any other damage.
Coil heaters are straight but can be customized into any other shape and size. They usually have square, rectangular or round cross sections. However, different shapes also can be formed such as star wound, spiral wound, closed coils or straight cables. Straight cables are made to pass through the equipment. Close coils offer optimal heat distribution. Spiral wound heaters are low profile heaters that generate high temperature usually in restricted areas. Star wound coils are inserted into pipes to create a turbulent flow in air that creates heat. Most of the coil heaters operate by AC voltage however; they can be operated on single phase or three phase voltage. Coil heaters are determined by the dimensions such as inner diameter, outer diameter, length, and width of the heating coil.
The coil heaters are configured on the termination basis. These heaters can be connected through plug configuration, terminal boxes, armored cables, metal over braids, and plain leads.
The coil heaters have a layered heating element which is mostly insulated with nickel chromium alloy that gives a good resistive properties and also produces heat. Insulated materials are ceramics, mica, magnesium oxide, fluoropolymer and fiberglass. The sleeve material can be aluminum, brass, iron, nickel alloy, rubber, stainless steel, and steel.
Duct heaters are used to generate heat in moving gas streams. These heaters are installed in the middle of the gas stream and generate forced flow heat convection. These heaters also emit radiation and heat up the other parts using thermal energy from the heater. This method of heating is best for molding, baking, drying and preheating solid objects. Duct heaters are designed in such a way that they can withstand explosions and can be easily used in hazardous locations.
The specifications of duct heaters are the same as all others. These are maximum operating temperature, heating capacity, maximum air flow and sheath material. The dimensions to follow for duct heaters are height, width and length of the heater.
The heating elements of duct heaters are open coil, tubular, and finned. Sheath insulation is the same as others that are ceramic, fiberglass, mica, or no insulation. Open coil heating elements are insulated with ceramic material that is used to isolate resistive heating elements. They prove an economically good choice for heating inert and non corrosive gases when the insulation is not required. Tubular heating elements are used for insulation as well as a protective barrier. These heaters are good to use in areas where temperatures are high and air flow is also high. Finned elements are used in closed spaces, as they have large fins that help in high heat dispersion.
Immersion heaters are the type of heaters that are placed in the substance that is needed to be heated. These heaters are placed in the liquid which heats up the liquid in return. These are particularly equipped with pipe threads, flanges and other mounting hardwares. Immersion heaters are explosion proof and can be used easily in hazardous conditions. Other specifications of immersion heaters are performance specifications, heat capacity, density, and sheath material.
Mechanical specifications of immersion heaters are necessary. These include mounting options, flanges or thread diameter, heated length and number of elements. Immersion heater comes with either threaded or flange mounting options. The number of heating elements also varies based on specifications. The number of heating elements increases the heating capacity of the heater.
Immersion heaters have different types of sleeve and sheath material that protects the heater from shocks. The insulation materials are iron, nickel alloy, steel, stainless steel, aluminum, brass, copper, and synthetic rubber. Steel sheath has a maximum temperature of 400°C and is used to heat oils. Copper has a maximum temperature of 180°C and is used for heating water that is municipal only. Nickel alloys have a temperature ranging from 760°C to 870°C and are used to heat water, strong and radiant alkaline solutions, air and gases. Stainless steel has a temperature of 650°C and is used to heat deionized and process water and some acids.
Flexible heaters are usually carved, screen printed, or wound around the heater which can be bent and flexed easily. This helps to confirm the surface area of the heater that is to be heated. There are many types of flexible heaters such as silicone rubber, kapton film heaters, carbon printed heaters, and transparent heaters. All these heaters are of different specifications and can be customized in any shape and color. These heaters are uneven, efficient, reliable, and accurate with good moisture and chemical resistant properties. They are flexible in nature and so they can be adhered to any kind of substrate. This flexibility made these heaters highly adaptable in a variety of industrial, commercial, and military applications. Flexible heaters are thin, light weight and are suitable to work in all kinds of harsh environments and vacuum applications also. The maximum operating temperature of flexible heaters is 260°C. For continuous use its temperature is 200°C.
Successful heating applications depend on the effective and efficient heat transfer. Flexible heaters work effectively by adjusting itself on the substance that requires heat. In this way the energy is not lost and ensures the complete transfer of thermal energy from the heating elements. Flexible heaters if designed correctly and installed perfectly then there will be a uniform heat transfer. The best part of these flexible heaters is that they are incorporated with different sensors and temperature controls such as thermostats, thermal fuses, thermo resistors, and other electronic components.
Kapton heaters or polyamide is a thin lightweight polymer film that provides great tear resistance, tensile strength, and dimensional stability. These heaters are used along flexible heaters and provide good resistance to fungus, radiations, and many other substances. This heater foil has circuit patterns that lower the production cost and give off the best heating experience. Kapton heaters have excellent thermal and dimensional stability. This material is even used in space, as it has good vacuum performance. Kapton heaters are resistant to chemicals, acids and other solvents. Good adhesive properties of kapton heaters make them suitable to join with metals. Kapton heaters base material can be joined with other alloys such as nickel, copper or iron. The density of kapton heaters is twice the watt density of other heaters.
Silicon rubber heaters are wire wound or etched foil. If they are wire wound then resistance wire is coiled around on a fiberglass cord for stability and support. These foil heaters are made up of thin metal foil, with a wire wound of smaller to medium size.
Silicon rubber heaters are wire wound and provide a great strength to withstand the flex without compromising the life and performance of these heaters. Silicon heaters are the best for any three dimensional shape, though any shape can be made by these heaters. The termination options are ring terminal and spade terminal. Many materials are used for sleeving and protecting the silicon heaters such as rubber sleeve and fiberglass sleeve.
Strip heaters are made by heating elements, sheath and a mounting hardware. The strip heaters have fins that help to radiate the heat to maximum area. They are bolted or clamped on the objects or on the walls so that they can cover maximum area for heat transfer. These are indoor heaters that are used for cabinet warming, baking ovens, and also used for vacuum dehydration. Strip heaters work by heating the sheet of thermoplastic over an electric element. Once the plastic sheet is melted then it can be bent into any kind of shape. These heaters are made of thermoplastics such as acrylic. Strip heaters use convection mode of heating. These are the clamping heaters with an operating temperature of 1200°C.
Foil heaters are self-contained pieces with heating elements encased between two aluminum foils. These heaters are best suited for surface heating applications. Sheath temperature is 300°F with a length range of 4”-60”. Foil heaters are also available with thermostats and with many cut outs available. Foil heaters are also available with low voltages and also with voltages of 120 or 240 volts. Foil heaters are constructed with different layers which are aluminum foil, insulating sleeve, premium grade resistant element and insulated leads. Foil heaters are of three types: self adhering, mechanically fastened (flexible), and mechanically fastened (semi rigid). There are different types of terminals for its connection such as flexible leads, straight quick connection, flag quick terminals, and spade terminals.
Electric heating has both advantages and disadvantages. In this chapter we will discuss the pros and cons of electric heaters.
A cartridge heater is a cylindrical tubular heating device that provides concise and precise heating for various forms of materials, machinery, and equipment. Unlike an immersion heater, a cartridge heater is inserted into a hole in the item to be heated to furnish internal radiant heat...
Ceramic heaters are electric heaters that utilize a positive temperature coefficient (PTC) ceramic heating element and generate heat through the principle of resistive heating. Ceramic materials possess sufficient electrical resistance and...
An immersion heater is a fast, economical, and efficient method for heating liquids in tanks, vats, or equipment. Known as bayonet heaters, they have heating elements that can be directly inserted into a container of water, oil, or other material in order to heat the entire contents...
Infrared heating is a heating method used to warm surrounding bodies by infrared radiation. Thermal energy is transferred directly to a body with a lower temperature through electromagnetic waves in the infrared region...
Radiant heaters are systems that generate heat internally and then radiate it to the nearby objects and people. The sun is a basic example of a radiant heater. When we feel warm on our bodies on a sunny day...
The idea of an electric heater seems to be out of place in modern society since most buildings have a sophisticated central heating system. That may be true, but electric heaters can be a helpful way of saving energy while providing efficient heating...
A heating element is a material or device that directly converts electrical energy into heat or thermal energy through a principle known as Joule heating. Joule heating is the phenomenon where a conductor generates heat due to the flow of electric current...